Detection of gram-negative bacteria in urine by the chromogenic limulus assay

A new kinetic single-stage Limulus amoebocyte lysate method for the detection of endotoxin in water and plasma

A convenient kinetic chromogenic Limulus amoebocyte lysate (LAL) method, based on components originally intended for a two-stage end-point method, has been developed. The components (LAL and chromogenic substrate) can be pooled and subsequently used in a single-stage kinetic procedure adapted to microplates. With the help of a kinetic software, it is possible to measure over the three log range 0.005-12 EU/ml in one test run--a range considerably wider than the range of the end-point procedure. A good linearity of the log-log standard curve, reflected by coefficients of regression between 0.997 and 1.0, is shown as well as a high-resolution (> 700 s) between the negative control and the lowest standard point. Moreover a good precision (C.V. < 10%) is obtained in both water and plasma, showing the usefulness of the method in different applications. Finally, a strong correlation (r = 0.95-0.99) to other LAL methods is demonstrated.

Significance of urinary endotoxin concentration in patients with urinary tract infection

Endotoxin is a component of the outer membrane of gram-negative rods (GNR). Since GNR are responsible for the majority of urinary tract infection (UTI), we measured the concentration of endotoxin in urine using chromogenic endotoxin-specific assay and examined its diagnostic utility in patients with suspected UTI. In all 18 urine samples with an endotoxin concentration exceeding 350 pg/ml and 2 samples with 10-350 pg/ml of endotoxin concentration, GNR were detected at a count of 10(4) cfu/ml. Negative for endotoxin were 3 samples of culture positive for gram-positive cocci (GPC), 2 samples containing various bacterial contaminants and all 37 samples with no growth on culture. Two urine samples collected 5 h after antibiotic dosage showed negative culture for GNR but a significant concentration of endotoxin. In an in vitro experiment, a residual concentration of antibiotic in urine inhibited bacterial growth, leading to a false-negative culture. These results suggest that chromogenic endotoxin assay is a reliable method for diagnosing UTI caused by GNR and detecting false-negative culture of GNR.